1. Field of the Invention
The present invention relates to an internal combustion engine, more particularly to an internal combustion engine including a cylinder block containing an oil return space in which a plurality of oil return passages provided in a cylinder head and for returning oil to an oil pan join together in a cylinder head.
2. Description of Related Art
There has been known an internal combustion engine including a cylinder block containing an oil return space in which a plurality of oil return passages provided in a cylinder head join together (see Japanese Patent Application Publication No. 2001-207816 (JP 2001-207816 A), for example)
The internal combustion engine disclosed in the aforementioned JP2001-207816 includes a cylinder block, a cylinder head arranged on the top of the cylinder block, and an oil pan arranged on the bottom of the cylinder block. The cylinder block includes four cylinder bores. A water jacket is provided on the outer periphery of the four cylinder bores so that it surrounds the four cylinder bores. Five oil return passages are provided outside the water jacket such that they are spaced at a predetermined distance. These oil return passages are formed so that they extend along an axial direction of the cylinder bores.
Of five oil return passages, the oil return passage disposed at the most distal end of the cylinder block is connected to a bypass groove in which oil flows in the column direction of the cylinder bores. Oil dropping from the cylinder head drops to the bypass groove and the oil return passage in the cylinder block.
To achieve an increased output of the internal combustion engine, the oil cooling performance has to be improved in accordance with the increase of the output. Furthermore, to improve the cooling performance, it is necessary to secure a sufficient oil flow rate in the oil return space to accelerate heat exchange between the oil and the water jacket in the cylinder block.
However, as regards the internal combustion engine disclosed in the above JP2001-207816, securing of the oil flow rate in the oil return passage (oil return space) of the cylinder block has not been mentioned or suggested. Therefore, it is considered that the internal combustion engine of JP2001-207816 can not achieve sufficiently accelerating of heat exchange between oil and the water jacket. Thus, there is a possibility that no sufficient cooling performance can be secured. Particularly, in case where multiple flows of oil dropping from the cylinder head join together in the oil return passage (oil return space) of the cylinder block, the oil flow rate sometimes may be reduced at a junction.